Various types of monitoring systems can effectively use detectors which indicate the presence of human beings in a predetermined region. These include, intrusion monitoring systems, HVAC systems, ambient condition monitoring systems such as fire or gas detecting systems, and limited mobility/elder persons assistance systems.
Fire detection systems usually include a plurality of devices including sensing devices, initiating modules and sounders connected to a main control panel. In case of danger/fire the control panel, according to it's settings, can initiate an evacuation procedure using audio and visual devices, call fire departments and, in case of sensitive areas, initiate operation of automatic extinguishment systems for example, CO2 gas release systems.
In many applications such as hotel rooms, hospitals or elderly residences, human presence tracking and localization is useful to reduce time to evacuation. Moreover when automatic extinguisher systems are in place such systems would be a means to reduce risk of asphyxiation/intoxication if extinguisher gases are released whilst persons are present.
In order to detect that a person is present in an indoor environment, numerous technical solutions based on a large variety of physical phenomena are available. Apart from the widespread use of passive infrared (PIR) detectors, which usually require motion to detect a person, low frequency/pressure responsive acoustic sensors, active systems using infrared light, ultrasound or microwaves can also be used. Also video cameras are widely applied in security systems.
Various access control systems including electronic keys (transponders, touch memory and systems for biometrical identification (fingerprint recognition, handwriting recognition, etc.) are also available.
Emitted radiant energy offers a basis to sense human presence. All objects are composed of continually vibrating atoms, with higher energy atoms vibrating more frequently. The vibration of all charged particles, including these atoms, generates electromagnetic waves. The higher the temperature of an object, the faster the vibration, and thus the higher the frequency of spectral radiant energy. As a result, all objects are continually emitting radiation at a rate with a wavelength distribution that depends upon the temperature of the object and its spectral emissivity.
Radiant emission is usually treated in terms of the concept of a blackbody. A blackbody is an object that absorbs all incident radiation and, conversely according to the Kirchhoff's law, is a perfect radiator. The energy emitted by a blackbody is the maximum theoretically possible for a given temperature. The radiative power (or number of photon emitted) and its wavelength distribution are given by the Planck radiation law:
                              W          ⁡                      (                          λ              ,              T                        )                          =                                                            2                ⁢                π                ⁢                                                                  ⁢                                  hc                  2                                                            λ                5                                      ⁡                          [                                                exp                  ⁡                                      (                                          hc                                              λ                        ⁢                                                                                                  ⁢                        kT                                                              )                                                  -                1                            ]                                            -            1                                                        W          /                      (                                          cm                2                            ⁢              µm                        )                          ,            where λ is the wavelength, T is the temperature, h is the Planck's constant, c is the velocity of light, and k is the Boltzmann's constant.
Human bodies are very good IR sources. The temperature of a typical human body is about 37° C. or 98° F. There is a constant heat exchange between the body and the environment due to the difference in their temperatures. The radiation characteristics of any object can be analyzed using the blackbody radiation curve governed by Planck's law.
For a typical human body, this curve is shown in FIG. 1. In FIG. 1, essentially all of the radiation is in the IR region with the peak radiation occurring at about 9.4 μm. The amount of power that the human body radiates within the wavelength range of interest is determined by integrating the blackbody radiation curve, FIG. 1, over this range.
There is a continuing need to be able to sense the presence of humans in regions of interest particularly in the presence of dangerous, or alarm conditions. In some environments, location, in addition to just presence detection, is important. Preferably detectors usable for sensing presence and/or location of individuals could be incorporated into regional monitoring, or alarm systems such as fire or gas detection systems, to provide another source of information to system operators as well as to first responders.